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binutils-gdb/gdb/i387-tdep.h
Andrew Burgess 8ee22052f6 gdb/x86: Handle kernels using compact xsave format 
For GNU/Linux on x86-64, if the target is using the xsave format for
passing the floating-point information from the inferior then there
currently exists a bug relating to the x87 control registers, and the
mxcsr register.

The xsave format allows different floating-point features to be lazily
enabled, a bit in the xsave format tells GDB which floating-point
features have been enabled, and which have not.

Currently in GDB, when reading the floating point state, we check the
xsave bit flags, if the feature is enabled then we read the feature
from the xsave buffer, and if the feature is not enabled, then we
supply the default value from within GDB.

Within GDB, when writing the floating point state, we first fetch the
xsave state from the target and then, for any feature that is not yet
enabled, we write the default values into the xsave buffer.  Next we
compare the regcache value with the value in the xsave buffer, and, if
the value has changed we update the value in the xsave buffer, and
mark the feature enabled in the xsave bit flags.

The problem then, is that the x87 control registers were not following
this pattern.  We assumed that these registers were always written out
by the kernel, and we always wrote them out to the xsave buffer (but
didn't enabled the feature).  The result of this is that if the kernel
had not yet enabled the x87 feature then within GDB we would see
random values for the x87 floating point control registers, and if the
user tried to modify one of these register, that modification would be
lost.

Finally, the mxcsr register was also broken in the same way as the x87
control registers.  The added complexity with this case is that the
mxcsr register is part of both the avx and sse floating point feature
set.  When reading or writing this register we need to check that at
least one of these features is enabled.

This bug was present in native GDB, and within gdbserver.  Both are
fixed with this commit.

gdb/ChangeLog:

	* common/x86-xstate.h (I387_FCTRL_INIT_VAL): New constant.
	(I387_MXCSR_INIT_VAL): New constant.
	* amd64-tdep.c (amd64_supply_xsave): Only read state from xsave
	buffer if it was supplied by the inferior.
	* i387-tdep.c (i387_supply_fsave): Use I387_MXCSR_INIT_VAL.
	(i387_xsave_get_clear_bv): New function.
	(i387_supply_xsave): Only read x87 control registers from the
	xsave buffer if the feature is enabled, and the state will have
	been written, otherwise, provide a suitable default.
	(i387_collect_xsave): Pre-clear all registers in xsave buffer,
	including x87 control registers.  Update control registers if they
	have changed from the default value, and mark features as enabled
	as required.
	* i387-tdep.h (i387_xsave_get_clear_bv): Declare.

gdb/gdbserver/ChangeLog:

	* i387-fp.c (i387_cache_to_xsave): Only write x87 control
	registers to the cache if their values have changed.
	(i387_xsave_to_cache): Provide default values for x87 control
	registers when these features are available, but disabled.
	* regcache.c (supply_register_by_name_zeroed): New function.
	* regcache.h (supply_register_by_name_zeroed): Declare new
	function.

gdb/testsuite/ChangeLog:

	* gdb.arch/amd64-init-x87-values.S: New file.
	* gdb.arch/amd64-init-x87-values.exp: New file.
2018-05-08 18:03:46 +01:00

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/* Target-dependent code for the i387.
Copyright (C) 2000-2018 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef I387_TDEP_H
#define I387_TDEP_H
struct gdbarch;
struct frame_info;
struct regcache;
struct type;
struct ui_file;
/* Number of i387 floating point registers. */
#define I387_NUM_REGS 16
#define I387_ST0_REGNUM(tdep) ((tdep)->st0_regnum)
#define I387_NUM_XMM_REGS(tdep) ((tdep)->num_xmm_regs)
#define I387_NUM_XMM_AVX512_REGS(tdep) ((tdep)->num_xmm_avx512_regs)
#define I387_MM0_REGNUM(tdep) ((tdep)->mm0_regnum)
#define I387_NUM_YMM_REGS(tdep) ((tdep)->num_ymm_regs)
#define I387_YMM0H_REGNUM(tdep) ((tdep)->ymm0h_regnum)
#define I387_BND0R_REGNUM(tdep) ((tdep)->bnd0r_regnum)
#define I387_BNDCFGU_REGNUM(tdep) ((tdep)->bndcfgu_regnum)
/* Set of constants used for 32 and 64-bit. */
#define I387_NUM_MPX_REGS 6
#define I387_NUM_BND_REGS 4
#define I387_NUM_MPX_CTRL_REGS 2
#define I387_NUM_K_REGS 8
#define I387_NUM_PKEYS_REGS 1
#define I387_PKRU_REGNUM(tdep) ((tdep)->pkru_regnum)
#define I387_K0_REGNUM(tdep) ((tdep)->k0_regnum)
#define I387_NUM_ZMMH_REGS(tdep) ((tdep)->num_zmm_regs)
#define I387_ZMM0H_REGNUM(tdep) ((tdep)->zmm0h_regnum)
#define I387_NUM_YMM_AVX512_REGS(tdep) ((tdep)->num_ymm_avx512_regs)
#define I387_YMM16H_REGNUM(tdep) ((tdep)->ymm16h_regnum)
#define I387_FCTRL_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 8)
#define I387_FSTAT_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 1)
#define I387_FTAG_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 2)
#define I387_FISEG_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 3)
#define I387_FIOFF_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 4)
#define I387_FOSEG_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 5)
#define I387_FOOFF_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 6)
#define I387_FOP_REGNUM(tdep) (I387_FCTRL_REGNUM (tdep) + 7)
#define I387_XMM0_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 16)
#define I387_XMM16_REGNUM(tdep) ((tdep)->xmm16_regnum)
#define I387_MXCSR_REGNUM(tdep) \
(I387_XMM0_REGNUM (tdep) + I387_NUM_XMM_REGS (tdep))
#define I387_YMM0_REGNUM(tdep) (I387_MXCSR_REGNUM(tdep) + 1)
#define I387_YMMENDH_REGNUM(tdep) \
(I387_YMM0H_REGNUM (tdep) + I387_NUM_YMM_REGS (tdep))
#define I387_MPXEND_REGNUM(tdep) \
(I387_BND0R_REGNUM (tdep) + I387_NUM_MPX_REGS)
#define I387_KEND_REGNUM(tdep) \
(I387_K0_REGNUM (tdep) + I387_NUM_K_REGS)
#define I387_ZMMENDH_REGNUM(tdep) \
(I387_ZMM0H_REGNUM (tdep) + I387_NUM_ZMMH_REGS (tdep))
#define I387_YMMH_AVX512_END_REGNUM(tdep) \
(I387_YMM16H_REGNUM (tdep) + I387_NUM_YMM_AVX512_REGS (tdep))
#define I387_XMM_AVX512_END_REGNUM(tdep) \
(I387_XMM16_REGNUM (tdep) + I387_NUM_XMM_AVX512_REGS (tdep))
#define I387_PKEYSEND_REGNUM(tdep) \
(I387_PKRU_REGNUM (tdep) + I387_NUM_PKEYS_REGS)
/* Print out the i387 floating point state. */
extern void i387_print_float_info (struct gdbarch *gdbarch,
struct ui_file *file,
struct frame_info *frame,
const char *args);
/* Return nonzero if a value of type TYPE stored in register REGNUM
needs any special handling. */
extern int i387_convert_register_p (struct gdbarch *gdbarch, int regnum,
struct type *type);
/* Read a value of type TYPE from register REGNUM in frame FRAME, and
return its contents in TO. */
extern int i387_register_to_value (struct frame_info *frame, int regnum,
struct type *type, gdb_byte *to,
int *optimizedp, int *unavailablep);
/* Write the contents FROM of a value of type TYPE into register
REGNUM in frame FRAME. */
extern void i387_value_to_register (struct frame_info *frame, int regnum,
struct type *type, const gdb_byte *from);
/* Size of the memory area use by the 'fsave' and 'fxsave'
instructions. */
#define I387_SIZEOF_FSAVE 108
#define I387_SIZEOF_FXSAVE 512
/* Fill register REGNUM in REGCACHE with the appropriate value from
*FSAVE. This function masks off any of the reserved bits in
*FSAVE. */
extern void i387_supply_fsave (struct regcache *regcache, int regnum,
const void *fsave);
/* Fill register REGNUM (if it is a floating-point register) in *FSAVE
with the value from REGCACHE. If REGNUM is -1, do this for all
registers. This function doesn't touch any of the reserved bits in
*FSAVE. */
extern void i387_collect_fsave (const struct regcache *regcache, int regnum,
void *fsave);
/* Fill register REGNUM in REGCACHE with the appropriate
floating-point or SSE register value from *FXSAVE. This function
masks off any of the reserved bits in *FXSAVE. */
extern void i387_supply_fxsave (struct regcache *regcache, int regnum,
const void *fxsave);
/* Similar to i387_supply_fxsave, but use XSAVE extended state. */
extern void i387_supply_xsave (struct regcache *regcache, int regnum,
const void *xsave);
/* Fill register REGNUM (if it is a floating-point or SSE register) in
*FXSAVE with the value from REGCACHE. If REGNUM is -1, do this for
all registers. This function doesn't touch any of the reserved
bits in *FXSAVE. */
extern void i387_collect_fxsave (const struct regcache *regcache, int regnum,
void *fxsave);
/* Similar to i387_collect_fxsave, but use XSAVE extended state. */
extern void i387_collect_xsave (const struct regcache *regcache,
int regnum, void *xsave, int gcore);
/* Extract a bitset from XSAVE indicating which features are available in
the inferior, but not yet initialised. */
extern ULONGEST i387_xsave_get_clear_bv (struct gdbarch *gdbarch,
const void *xsave);
/* Prepare the FPU stack in REGCACHE for a function return. */
extern void i387_return_value (struct gdbarch *gdbarch,
struct regcache *regcache);
/* Set all bnd registers to the INIT state. INIT state means
all memory range can be accessed. */
extern void i387_reset_bnd_regs (struct gdbarch *gdbarch,
struct regcache *regcache);
#endif /* i387-tdep.h */
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